In U.S. Ser. No. 341,830 a fold-up portable ladder is disclosed which comprises a plurality of U-shaped sections, that form both the rungs and side rails of a ladder when assembled. Each section is attached and hinged at its lower portion to the next adjacent section. Positioned below each of said hinges are latches adapted to fit into and mate with an aperture located in the vertical wall of the said next adjacent section, the lowest of said u-shaped sections beieng the widest and the top uppermost of said u-shaped sections being the narrowest and each of said sections in between being progressively narrower as they approach the top section. The latches are spring loaded so that when aligned with and mated into said aperture they will remain in place and securely hold each rung in position. To disengage each latch, there is positioned in each horizontal rung portion a spring and an external latch or spring release. When the pair of latch or spring releases are pinched together, the latch is forced away from said apertures and releases each U-shaped section from the next adjacent section. The vertical arms of each U-shaped section thus are connected to and aligned with the next section by the use of latches located in the horizontal base of each U-shaped section. The latches in the horizontal base fit into the orifice or aperture in each vertical section adjacent to it. Each aperture has tapered grooves or slide portions that allow the latches to slip into the aperture easily when setting the ladder up for use. Also, the tips of each latch portion is tapered to conform to the configuration of each orifice or aperture slide portion that facilitates the movement of the latch into the aperture. The spring releases need not be manipulated when setting up the ladder, only when the ladder is to be folded up after use.
In U.S. Ser. No. 492,487 a portable fold-up ladder is disclosed having spring rung releases that comprise two means that are pinched together (FIGS. 1B, 2, 3A, and 3B). Also, in the same application in FIG. 3C a single means spring release is disclosed wherein ring 24 is turned or pulled to release the modules from each other. In this U.S. Ser. No. 492,487 each section or module of the ladder is attached and hinged at its lower portion to the next adjacent wider section, the wider modules or sections are movably positioned below each of the narrower modules. Below said hinges are locking latches to fit into and mate with an aperture located in the vertical wall of the said next adjacent section, the lowest of said U-shaped modules or sections being the widest and the top uppermost of said U-shaped sections being the narrowest. Each of said sections in between the top and lowest sections are progressively narrower as they approach the said top section. The latches are spring loaded so that when aligned with and mated into the aperture they will remain in place and securely hold each module in position. To disengage each module, there is positioned in each horizontal rung portion a spring and an external latch release. When the pair of latch releases of FIGS. 3A and 3B are pinched together, the latches are forced away from said apertures and releases each U-shaped section from the next adjacent section. Alternatively, when the release 24 (of FIG. 3C) is turned or pulled the latches are forced away from said apertures and releases each U-shaped section from the next adjacent section. The vertical or upright arms of each U-shaped section thus are connected to and aligned with the next section by the use of latches located in the horizontal base of each U-shaped section. The latches in the horizontal base are aligned with and fit into the orifice or aperture in each vertical section adjacent to it. Also, the tips of each latch portion are tapered at their ends for easy sliding into each orifice or aperture. The latch releases need not be manipulated when setting up the ladder, only when the ladder is to be folded up after use.
In Ser. No. 537,276 several latch release means are disclosed, a central rung release means as shown in FIGS. 1A and 1B, an outer module side release means shown in FIGS. 2A, 2B and 3, an inner module side release means shown in FIGS. 2A and 4, and a terminal rung release means as shown in FIG. 5. Each section or module is attached and hinged at its lower portion to the next adjacent wider section, the wider modules or sections are movably positioned below each of the narrower modules. Below or above said hinges are locking latches or slide bolts located in either the vertical side rails or any lower portion of the module adapted to fit into and mate with an aperture located in the upper portion or vertical rail of the said next wider adjacent section, the lowest of said U-shaped modules or sections being the widest and the top uppermost of said U-shaped sections being the narrowest. Each of said sections in-between the top and lowest sections are progressively narrower as they approach the said top section. The latches or bolts are spring loaded so that when aligned with and mated into the aperture they will remain in place and securely hold each module in position. To disengage each module, there is positioned in each module lower portion (except the lowest module) a spring and an external latch or lock release. When the latch releases are turned or pulled or moved, the latch or bolt is forced away from said apertures and releases each U-shaped modular section from the next adjacent section. The vertical or upright arms of each U-shaped section thus are connected to and aligned with the next section by the use of latches and apertures in the lower portion of the narrower module and the upper portion of the wider module of each U-shaped section. The latches in the horizontal base are aligned with and fit into the orifice or aperture in each module section adjacent to it. Also, the tops of each latch portion are tapered at their ends for each sliding into each orifice or aperture. It is preferred the latches be spring loaded, however, a conventional slide bolt lock can be used. In using spring loaded locks, the latch releases need not be manipulated when setting up the ladder, only when the ladder is to be folded up after use. This is achieved by forming the ladder from metal that is at least partially eliptical, curved, or rounded in cross-section and from bolts or latches having rounded or tapered ends. In the ladder disclosed in Ser. No. 537,276 several modifications of locking mechanisms are disclosed. These are intended to be included in the present application.